1. Field of the Invention
The present invention relates to a dielectric resonator, a dielectric filter, a sharing device, and a communication apparatus which are used in a microwave band, a millimeter wave band, or the like.
2. Description of the Related Art
In recent years, a communication system achieving a large capacity and a high speed has been required in accordance with a rapid increase in demand of a mobile communication system or multimedia systems. With such an increase in amount of information to be communicated, a use frequency band has been extended from a microwave band to a millimeter wave band. Even in the millimeter wave band, a TE01xcex4 mode dielectric resonator constituted by a conventionally known cylindrical dielectric material can be used in a manner in the microwave band. At this time, severe processing precision is required because the resonance frequency of the TE01xcex4 mode dielectric resonator is determined depending on the external size of the cylindrical dielectric material. However, a precise size cannot be set with respect to the resonance frequency because of a factor such as contraction or the like of the dielectric material in sintering.
When a plurality of TE01xcex4 mode dielectric resonators are arranged at predetermined intervals in a metal case to constitute a dielectric filter, coupling between an input/output means such as a metal loop and a dielectric resonator or between dielectric resonators is determined by the distance therebetween. For this reason, the resonators and the like must be arranged at a high a positional precision.
Therefore, the present inventor proposes, in Japanese Patent Application No. 7-62625, a dielectric resonator which solves the above problems and is excellent in processing precision and a dielectric filter which is excellent in positional precision.
The basic arrangement of a dielectric filter according to this application is shown in FIG. 12. FIG. 12 is an exploded perspective view of the dielectric filter according to this application.
As shown in FIG. 12, a dielectric filter 101 is constituted by a dielectric substrate 102 and upper and lower conductive cases 103 and 104.
The dielectric substrate 102 is a substrate having a predetermined specific inductive capacity. An electrode 102a is entirely formed on one major surface of the substrate except for three circular openings 102c each having a predetermined size, and an electrode 102b is entirely formed on the other major surface except for three circular openings 102db each having a predetermined size. The three openings 102c in one major surface oppose the three openings 102d in the other major surface, respectively.
The upper conductive case 103 consists of a metal, and has a box-like shape which opens downward. The upper conductive case 103 is arranged near the openings 102c of the electrode 102a to be spaced apart from the dielectric substrate 102.
The lower conductive case 104 consists of a dielectric material, and has a box-like shape which opens upward and has flanges projecting from the side surfaces of the lower conductive case 104. A shielding conductor 106 is formed on the inner peripheral surface of the lower conductive case 104, and input/output electrodes 105a and 105b are formed at positions opposing both the end openings 102d of the three openings 102d of the electrode 102b such that the input/output electrodes 105a and 105b are insulated from the shielding conductor 106. The input/output electrodes 105a and 105b are led from holes 104a and 104b formed in the side surface of the lower conductive case 104. In addition, a spacer 107 for keeping a predetermined interval between the inner bottom surface of the lower conductive case 104 on which the shielding conductor 106 is formed and the dielectric substrate 102 is arranged in the lower conductive case 104. The spacer 107 consists of a dielectric material having a low dielectric constant not to disturb electromagnetic fields in the upper and lower conductive cases 103 and 104.
When this structure is used, electromagnetic field energy is confirmed by the dielectric substrate 102 near a portion sandwiched by the three openings 102c and 102d in which the electrode 102a opposes the electrode 102b, and three resonators can be achieved. For this reason, a dielectric filter having a three-stage resonator can be obtained.
With this arrangement, since a resonance region can be defined by the size of an opening portion of an electrode, a method such as etching can be used, and a dielectric filter which can extremely accurately reproduce dimensional precision of a resonator with respect to a resonance frequency and positional precision between resonances can be formed.
However, an unnecessary TEM mode electromagnetic wave may be generated by the electrode edge portions of the openings of the electrodes 102a and 102b formed on the dielectric substrate 102. Such a TEM wave transmits between the electrodes 102a and 102b formed on the dielectric substrate 102 to be reflected by the end face of the dielectric substrate 102 to generate a standing wave, so that resonance occurs in the structure. This standing wave operates as a spurious output with respect to the filter characteristics of the dielectric filter 101 itself to affect the out-of-band characteristics of the filter. As a result, the filter characteristics of the dielectric filter 101 itself may be degraded.
An unnecessary TEM mode electromagnetic wave generated by the electrode edge portions of the openings of the electrodes 102a and 102b formed on the dielectric substrate 102 transmits between the electrode 102a and the conductor 104a or the electrode 102b and the conductor 104b to be reflected by the end portion of the dielectric substrate 102 to generate a standing wave, so that resonance occurs in the structure. This standing wave also operates as a spurious output with respect to the filter characteristics of the dielectric filter 101 itself to affect the out-of-band characteristics of the filter. As a result, the filter characteristics of the dielectric filter 101 itself may be degraded.
The present invention has been made to solve the above problems, and has as its object to provide a dielectric filter which can suppress a spurious output acting as unnecessary resonance to prevent the out-of-band characteristics of the filter from being degraded.
A dielectric resonator according to the first aspect comprises a dielectric substrate, a first conductor formed on one major surface of the dielectric substrate, a second conductor formed on the other major surface of the dielectric substrate, a first opening formed in the first conductor to expose the dielectric substrate from the first conductor, a second opening formed in the second conductor to expose the dielectric substrate from the second conductor, a first conductive plate arranged to be spaced apart from the first conductor and to cover at least the first opening, a second conductive plate arranged to be spaced apart from the second conductor and to cover at least the second opening, a resonance portion determined by the first opening and the second opening, and an electromagnetic wave absorbing member arranged between the first and second conductive plates.
In this manner, an electromagnetic wave in a mode in which unnecessary resonance occurs can be absorbed by the electromagnetic wave absorbing member.
In a dielectric resonator according to the second aspect, the electromagnetic wave absorbing member is arranged between at least one of the first and second conductive plates and the dielectric substrate.
In this manner, an unnecessary TEM mode electromagnetic wave generated by the electrode edge portions of the openings of the electrodes 102a and 102b formed on the dielectric substrate 102 and transmitting between the electrode 102a and the conductor 104a or the electrode 102b and the conductor 104b can be absorbed, and unnecessary resonance can be reduced.
In a dielectric resonator according to third aspect, the electromagnetic wave absorbing member is arranged to be in contact with a side surface perpendicular to both the major surfaces of the dielectric substrate.
In this manner, an unnecessary TEM mode electromagnetic wave generated by the electrode edge portions of the openings of the electrodes 102a and 102b formed on the dielectric substrate 102 and transmitting between the electrodes 102a and 102b can be absorbed, and unnecessary resonance can be reduced.
A dielectric filter according to the fourth aspect comprises a dielectric substrate, a first conductor formed on one major surface of the dielectric substrate, a second conductor formed on the other major surface of the dielectric substrate, a first opening formed in the first conductor to expose the dielectric substrate from the first conductor, a second opening formed in the second conductor to expose the dielectric substrate from the second conductor, a first conductive plate arranged to be spaced apart from the first conductor and to cover at least the first opening, a second conductive plate arranged to be spaced apart from the second conductor and to cover at least the second opening, a resonance portion determined by the first opening and the second opening, input/output means coupled to the resonance portion, and an electromagnetic wave absorbing member arranged between the first and second conductive plates.
In this manner, an electromagnetic wave in a mode in which a spurious output is generated can be absorbed by the electromagnetic wave absorbing member.
In a dielectric filter according to the fifth aspect, the electromagnetic wave absorbing member is arranged between at least one of the first and second conductive plates and the dielectric substrate.
In this manner, an unnecessary TEM mode electromagnetic wave generated by the electrode edge portions of the openings of the electrodes 102a and 102b formed on the dielectric substrate 102 and transmitting between the electrode 102a and the conductor 104a or the electrode 102b and the conductor 104b can be absorbed, and an unnecessary spurious output can be reduced.
In a dielectric filter according to the sixth aspect, the electromagnetic wave absorbing member is arranged to be in contact with a side surface perpendicular to both the major surfaces of the dielectric substrate.
In this manner, an unnecessary TEM mode electromagnetic wave generated by the electrode edge portions of the openings of the electrodes 102a and 102b formed on the dielectric substrate 102 and transmitting between the electrodes 102a and 102b can be absorbed, and an unnecessary spurious output can be reduced.
A sharing device according to the seventh aspect comprises: at least a first filter and a second filter; the first filter including a dielectric substrate, a first conductor formed on one major surface of the dielectric substrate, a second conductor formed on the other major surface of the dielectric substrate, a first opening formed in the first conductor to expose the dielectric substrate from the first conductor, a second opening formed in the second conductor to expose the dielectric substrate from the second conductor, a first conductive plate arranged to be spaced apart from the first conductor and to cover at least the first opening, a second conductive plate arranged to be spaced apart from the second conductor and to cover at least the second opening, a resonance portion determined by the first opening and the second opening, and input/output means coupled to the resonance portion, and the second filter including a dielectric substrate, a first conductor formed on one major surface of the dielectric substrate, a second conductor formed on the other major surface of the dielectric substrate, a first opening formed in the first conductor to expose the dielectric substrate from the first conductor, a second opening formed in the second conductor to expose the dielectric substrate from the second conductor, a first conductive plate arranged to be spaced apart from the first conductor and to cover at least the first opening, a second conductive plate arranged to be spaced apart from the second conductor and to cover at least the second opening, a resonance portion determined by the first opening and the second opening, and input/output means coupled to the resonance portion; common input/output means which connects one of the input/output means of the first filter to one of the input/output means of the second filter; and an electromagnetic wave absorbing member arranged at at least one of a position between the first and second conductive plates of the first filter and a position between the first and second conductive plates of the second filter.
In this manner, an electromagnetic wave in a mode in which a spurious output is generated can be absorbed by the electromagnetic wave absorbing member.
In a sharing device according to the eighth aspect, the electromagnetic wave absorbing member is arranged at at least one of a position between at least one of the first and second conductive plates of the first filter and the dielectric substrate and a position between at least one of the first and second conductive plates of the second filter and the dielectric substrate.
In this manner, an unnecessary TEM mode electromagnetic wave generated by the electrode edge portion of the opening of the electrode formed on the dielectric substrate and transmitting between the electrode and the conductor can be absorbed, and an unnecessary spurious output can be reduced.
In a sharing device according to the ninth aspect, the electromagnetic wave absorbing member is arranged to separate the resonance portion of the first filter and the resonance portion of the second filter from each other.
In this manner, resonance occurring in the resonance portion of the first filter and resonance occurring in the resonance portion of the second filter can be prevented from being interfered to each other.
In a sharing device according to the tenth aspect, the electromagnetic wave absorbing member is arranged to be in contact with at least one of a side surface perpendicular to both the major surfaces of the dielectric substrate of the first filter and a side surface perpendicular to both the major surfaces of the dielectric substrate of the second filter.
In this manner, an unnecessary TEM mode electromagnetic wave generated by the electrode edge portion of the opening of the electrode formed on the dielectric substrate and transmitting between the electrode and the conductor can be absorbed, and an unnecessary spurious output can be reduced.
A communication apparatus according to the eleventh aspect comprises at least a sharing device, a transmission circuit, a reception circuit, and an antenna, wherein the sharing device includes: a first filter having a dielectric substrate, a first conductor formed on one major surface of the dielectric substrate, a second conductor formed on the other major surface of the dielectric substrate, a first opening formed in the first conductor to expose the dielectric substrate from the first conductor, a second opening formed in the second conductor to expose the dielectric substrate from the second conductor, a first conductive plate arranged to be spaced apart from the first conductor and to cover at least the first opening, a second conductive plate arranged to be spaced apart from the second conductor and to cover at least the second opening, a resonance portion determined by the first opening and the second opening, and input/output means coupled to the resonance portion; a second filter having a dielectric substrate, a first conductor formed on one major surface of the dielectric substrate, a second conductor formed on the other major surface of the dielectric substrate, a first opening formed in the first conductor to expose the dielectric substrate from the first conductor, a second opening formed in the second conductor to expose the dielectric substrate from the second conductor, a first conductive plate arranged to be spaced apart from the first conductor and to cover at least the first opening, a second conductive plate arranged to be spaced apart from the second conductor and to cover at least the second opening, a resonance portion determined by the first opening and the second opening, input/output means coupled to the resonance portion; common input/output means which connects one of the input/output means of the first filter to one of the input/output means of the second filter; and an electromagnetic wave absorbing member arranged at at least one of a position between the first and second conductive plates of the first filter and a position between the first and second conductive plates of the second filter, the transmission circuit is connected to the first filter, the reception circuit is connected to the second filter, and the antenna is connected to the common input/output means.
In this manner, an electromagnetic wave in a mode in which a spurious output is generated can be absorbed by the electromagnetic wave absorbing member.
In a communication apparatus according to the twelfth aspect, the electromagnetic wave absorbing member is arranged at at least one of a position between at least one of the first and second conductive plates of the first filter and the dielectric substrate and a position between at least one of the first and second conductive plates of the second filter and the dielectric substrate.
In this manner, an unnecessary TEM mode electromagnetic wave generated by the electrode edge portion of the opening of the electrode formed on the dielectric substrate and transmitting between the electrode and the conductor can be absorbed, and an unnecessary spurious output can be reduced.
In a communication apparatus according to the thirteenth aspect, the electromagnetic wave absorbing member is arranged to separate the resonance portion of the first filter and the resonance portion of the second filter from each other.
In this manner, a signal on the reception side and a signal on the transmission side can be prevented from being interfered to each other.